Engineers around the world are scrambling to create next-generation batteries that are energy-efficient and easy to mass produce. One promising candidate is aqueous flow battery technology being developed at the University of Colorado.

The low-cost, high-performance batteries may one day lead to scalable grid-level storage for wind and solar energy. They use a key component that is abundant in nature—chromium—to achieve exceptional voltage and high efficiency.

“The materials are low-cost, nontoxic and readily available, offering future promise for cost-effective manufacturing,” says Michael Marshak, an assistant professor of chemistry who is heading up the research project. “Flow batteries get around the scaling problems associated with chemistries that rely on solid materials, such as lithium-ion.

“Although lithium-ion technology can provide power for smaller scale applications, you would need millions of batteries to backup even a small fossil fuel power plant for an hour,” notes Marshak, who also serves as a fellow at the University of Colorado’s Renewable and Sustainable Energy Institute. “But, while lithium-ion chemistry is effective, it’s ill-suited to meet the capacity of an entire wind turbine field or solar panel array.

“The basic problem with lithium-ion batteries is that they don’t scale very well,” claims Marshak. “The more solid material you add, the more resistance you add and then all of the other components need to increase in tandem. So in essence, if you want twice the energy, you need to build twice the batteries. That’s just not cost-effective when you’re talking about this many megawatt hours.”

According to Marshak, aqueous flow batteries are a more promising alternative for renewable power grid applications. Flow batteries keep their active ingredients separated in liquid form in large tanks, allowing the system to distribute energy in a managed fashion, similar to the way a gas tank provides steady fuel combustion to a car’s engine.

Although flow batteries have been available for decades, they have struggled to gain a broad foothold in commercial and municipal grid operations due to their unwieldy size (they typically are as big as shipping containers), high operating costs and comparably low voltage. In addition, commercially available flow battery technology has traditionally been based on the element vanadium, which is relatively expensive for energy storage applications.

“There’s a real need for alternative materials that are less expensive,” says Marshak. “Renewable energy sources provide a growing share of U.S. electrical production, but currently lack a large-scale solution for storing harvested energy and redeploying it to meet demand during periods when the sun isn’t shining or the wind isn’t blowing.

“There are mismatches between supply and demand on the energy grid during the day,” Marshak points out. “The sun might meet the grid’s needs in the morning, but demand tends to peak in the late afternoon and continue into the evening after the sun has set. Right now, utility companies have to fill that gap by quickly revving up their coal and natural gas production, just like you’d take a car from zero to 60.”

To improve the performance of flow battery chemistry, Marshak and his colleagues combined organic binding agents, or chelates, with chromium ions to stabilize a potent electrolyte. The process creates a shield around the chromium electron, preventing water from hampering the reactant and allowing each of the battery cells to disperse 2.13 volts—nearly double the operational average for a flow battery.

Marshak plans to continue optimizing the technology and have it commercially available sometime within the next five years. “We will be scaling it up in the lab to cycle the battery for even longer periods of time,” he explains. “We also still have to do some long-term durability testing.

“We’ve solved the problem on a fundamental level,” says Marshak. “Now, there are a lot of things we can try to keep pushing the performance limit.”